The present invention relates to an audio circuit for a television receiver, and more particularly to an audio circuit for a television receiver based on a three-speaker system in which a left-hand speaker is disposed on the left side of the screen of the television receiver, a right-hand speaker is disposed on the right side of the screen, and a central speaker is disposed above or below the screen.
Among recent television receivers intended to reproduce the field of sound, some are designed to vary the frequency characteristics of the audio circuit in response to the content of the audio signal (e.g., a program mainly containing human voice, a program of music, or a program of cinema) or designed to have two or more speakers to form a multiple speaker system. One example is the "Dolby Pro Logic Sound System" described in an article entitled "Sanyo Dolby Pro Logic Sound Decoder IC" in "Television Technology", pp. 31-36, October, 1988. This system includes three speakers located on the left (L), right (R), and at the center (C) of the screen (for producing a total component of the left and right outputs), and further includes a surround speaker (S) at the rear of the audience (for producing a differential component of the left and right outputs). The system emphasizes the sound source positions and sound directions by producing the sound of a major signal at a highest power on the basis of comparison among the signals (L, R, C, S) delivered to the respective speakers. The system also includes an operational mode which involves only the left, right and central speakers, although the sound effect is degraded.
It is also known to have R, L and C speakers for a television receiver where the C speaker provides only a low frequency output of the signals applied to the L and R speakers in the range of 30-170 Hz, thereby providing a bass emphasis at the C speaker.
Although the foregoing systems are effective for clarifying the sound source positions and directions and the movement of sound, such systems lack in the ability of separation of a human voice from other sound such as background music.
Among various sound sources accompanying pictures displayed on the television screen, human voice is most significant in many cases, and emphasis on the human voice relative to background music, for example, is highly effective. Conversely, in the case of a picture displayed on a screen in which no actor is included or an actor is not the major object, the reduction of the frequency components of human voice is highly effective. Conventional systems are deficient with respect to the human voice and the following describes different situations with respect to consideration of the human voice.
In the case of a three-speaker system (left, right and central speakers) for reproducing the field of sound, when an actor speaks at the center of the screen in the presence of background music or the like, if the central speaker produces a sound of the signal which is merely the sum of the left-hand and right-hand speaker signals, both the human voice and music are coincident at the center speaker. In this case, if it is intended to produce a sound of high and low frequency components of music or the like on the left-hand and right-hand speakers, with only a human voice component being produced on the central speaker, a sound of significantly large output must be produced on the central speaker relative to the left and right outputs in order to have a sufficient effect, which results in an excessively large total sound output.
In the case of a program with a minor human voice, if the central speaker is kept active, stereo separation is deteriorated, or if matrix sound is employed to overlay the left-right differential component on the left-hand and right-hand speaker signals, sound other than human voice becomes too large.